Radicular post head comprising reversible retention and automatic positioning means

ABSTRACT

A radicular post cooperating with a resilient dental impression for use in preparing a cap to be fixed to a tooth having a post hole shaped to receive the post, each post having a conical part for entering the post hole and having a cylindrical part aligned on the longitudinal axis of the post and extending from the tooth when the post is seated in the post hole, the cylindrical parts of the posts having retention grooves circularly disposed around them, the parts of the posts being fully symmetrical about the axis; and the impression being formed of a cured resilient compound having a molded hole fitting the cylindrical part of each post, and the impression holes having resilient rings shaped to enter and fill the grooves in associated posts, the shapes of the grooves and rings and the resilience of the impression compound being selected such that the cylindrical parts of the posts can be removed from and re-positioned within the holes in the impressions without damaging the impressions and while achieving accurate positioning of the posts therein because the parts of the posts are symmetrical about their axes.

FIELD OF THE INVENTION

The invention described herein is a radicular post with aself-positioning head including a means for light and gentle retentionthat does not damage the dental impression. The invention concerns, inparticular, the fact that the same means serves both for light retentionand for self-positioning of the head of the radicular post in theimpression immediately after insertion in the prepared hole.

BACKGROUND OF INVENTION AND RELATED ART

At the present time, the majority of the heads of existing radicularposts or dowels are equipped with a retentive element designed to be aseffective as possible. Indeed, when an impression is to be taken of themouth, and once the root has been prepared and the intraradicular posthas been put in place, these retentive elements must maintain theradicular posts in place in the impression or negative and therebypermit withdrawal of the latter from the mouth. However, even if theradicular posts remain in the impression and are thus freed from theirroot, there is always the possibility that this technical withdrawalmaneuver will have caused slight displacement of said posts. Moreover,posts frequently remain stuck in place when impressions are taken in themouth. This results from the fact that the intraradicular portion of thepost in the tooth root offers a large contact surface and thus creates astrong retentive force whereas the contact surface of the head of thepost in the impression is relatively small.

In order to facilitate post withdrawal when impressions are taken in themouth, post manufacturers have equipped the heads of their radicularposts with highly effective retention elements. The resulting flattenedheads, ribbed heads, slotted heads and flanged heads are all designed toform a true means of anchorage in the impression compound (so called;i.e., "impression composition" (lit., "dental paste")). If, by accident,the head of a radicular post of one of these existing designs fails tolift out when an impression is taken in the mouth, it is virtuallyimpossible to replace said head in the impression.

Due to [sic] the shape of its head (flattened, ribbed, flanged), thepost lies at an angle with respect to its longitudinal axis. It istherefore impossible to determine the position the ribs or flanges werein. Furthermore, the impression compound will have been partially tornaway at this point. Prior to taking an impression, numerouspractitioners therefore place an index marker on the compound or on theradicular post itself in order to be able to redetermine the correctorientation should the post not lift out from the patient's mouth. Postsupports or prefabricated transfer elements have also been described:these are supplementary parts designed to automatically fasten the postduring impression taking, to provide precise indication of post positionduring manipulations thanks to index markings, to eliminate any error inpost positioning, and/or to hold the post in place while the impressionis taken. In practice, these additional parts [may] consist of a metalspring or slotted tube that fits onto the head of the post (see patentNo. FR 1 463 860 NARBONI).

SUMMARY OF THE INVENTION

The invention eliminates all of these drawbacks. The head of theradicular post features a means of light retention that does not damagethe impression and allows self-positioning of the head of the post inits housing (i.e., lit., "the cavity serving as a receptacle") in theimpression. For this purpose, the head of the radicular post includes aleast one continuous uniform circular groove. The number of grooves, aswell as the shape of the walls or sides and/or the bottom of thegrooves, are a function of the characteristics of the impressioncompound utilized. The circular groove must penetrate the impressioncompound in which it forms a ring of compound that serves as a clip andlocks the head of the post in place in the impression. This locking isreversible, due to the fact of the continuity [sic] of the uniformcircular groove, and due to the fact that the radicular post head is notoriented at an angle to the longitudinal axis. The shape of the groovecan vary as a function of the technical characteristics of theimpression compound used; the bottom of the groove may thus be eitherflat or cup-shaped. Likewise, the sides of the groove can form differentangles with the bottom of the groove, ranging from 90° to over 130°. Inaddition, the angles of the sides or walls are not necessarilyidentical, i.e. the angle formed by the groove bottom and the sideclosest to the top of the head may differ from the angle formed by thegroove bottom and the side closest to the intraradicular end of thepost.

The top of the head of the radicular post may be conical, pan-shaped (inthe shape of a truncated cone), round, rounded, spherical, hemisphericalor flat. A preferred embodiment of the invention comprises a radicularpost with a pan-shaped (or similar truncated) head: this shape allowsthe ejection or escape of serous fluids and mucus along the sides.Furthermore, thanks to the angles selected, a head with this shape topcan form a prepositioned housing with the impression of the sides of thegroove (which sides are parallel) that facilitates the automaticpositioning or replacement of the head of the post in the impression.

The accompanying figures, which are provided solely as examples and arenot exhaustive, make the invention easy to understand; these figuresshow a [sic] preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic side view of the radicular post in place in theimpression compound, with a sectional view of the housing.

FIG. 2 is a diagrammatic side view of the radicular post in placeopposite the impression compound, with a sectional view of the housingprior to insertion in the hole prepared in the impression compound.

FIG. 3 is a diagrammatic side view of the radicular post after removalfrom the hole prepared in the impression compound.

FIG. 4 is a diagrammatic side view of the radicular post in place in theimpression compound, with a sectional view of the housing. This viewreveals that post insertion and removal do not deform the impressioncompound.

FIG. 5 is a side view of the radicular post with two grooves or slots.

FIG. 6 is a side view of the radicular post with three grooves or slots.

FIG. 7 is a side view of the radicular post with four grooves or slots.

FIG. 8 is a side view of the radicular post with ten grooves or slots.

FIG. 9 is a close-up side view of the top of the head of the radicularpost, which is conical.

FIG. 10 is a close-up side view of the top of the head of the radicularpost, which is rounded.

FIG. 11 is a close-up side view of the top of the head of the radicularpost, which is flat.

FIG. 12 is a close-up sectional view of the head of the post showing, inparticular, the bottom of the groove and the angles of the sides of saidgroove.

DESCRIPTION OF PREFERRED EMBODIMENTS

The radicular post is inserted in the tooth root by the conical part(1), which is terminated by the intraradicular tip (2) of the post.

The cylindrical part of the radicular post, which forms the head (3), isequipped with a groove or slot (4); this groove (4) constitutes a meansof gentle retention which allows the impression compound (5) to serve asa clip by forming a ring (6) of compound in the groove or slot (4).

When an impression is taken, it is thus easy to understand why there isno problem even if the post or posts do not lift out with the impressionor the negative provided that posts of the design subject of the presentinvention are used.

The user need only recover the post or posts, without worrying abouttheir orientation and without fitting them with an index marker. Theuser need only insert the post in the corresponding prepared hole (8) inthe impression taken of the mouth and push it in until he feels a clicksignifying that the post is correctly in place.

As can be seen from FIG. 3, the fact that the post remained in place inthe tooth root did not deteriorate the impression compound (5).

The head (3) of the radicular post features a means for gentleretention: it does not remove any of the impression compound (5) when it(the post) is removed from its housing (7) and does not damage theimpression, as occurs with posts of existing design. Furthermore, theunit is self-positioning; as shown by FIG. 2, it suffices to introducethe radicular post into its prepared hole (8) by the head (3) and topush it in until a click is felt. Due to the shape of the head (3) ofthe radicular post, the user does not have to worry about the angularorientation of the post with respect to its housing (7) or about thedepth of insertion in the housing (7); thanks to the presence of one ormore grooves, the user knows whether or not the post is correctly inplace in its housing (7).

All of the above is impossible with posts of existing design which havea highly retentive head which can damage the impression compound;furthermore, the presence of the retentive elements (ribs or theircounterparts) means that the head is asymmetrical, and must be fittedwith an index marker or marked itself to indicate the correct position.

The post as designed by the invention thus eliminates all risks of errorin positioning and in replacement, without damage to the impression,during all of the technical maneuvers required both in the dentallaboratory and when the impression is taken in the mouth.

FIGS. 5, 6, 7 and 8 show heads (3) of radicular posts equipped with twoor more continuous uniform circular grooves (4) which form rings ofcompound (6) that serves as clips. All of these post heads have the sametechnical characteristics: the presence of one or more grooves (4)depending on the impression compound utilized, since some such compoundsare more flexible.

FIGS. 9, 10 and 11 show the tops (9) of heads of radicular posts. Top(9a) is conical, top (9b) is rounded and top (9c) is flat.

The shape of the groove (4) may vary, depending on the technicalcharacteristics of the impression compound (5) employed; thus, thebottom (10) of the groove (4) may be either flat (10a) or U-shaped [incross section] (10b) (see FIG. 12). Moreover, the sides (11) and (12) ofthe groove (4) can form with said bottom (10) (10a or 10b) an angle A1and an angle A2 that can vary from 90° to over 130°. Angles A1 and A2 ofthe sides (11) and (12) need not be identical: the side (12) which isnearest to the top (9) of the head (3) can form an angle different fromthat formed by side (11) which is nearest to the intraradicular tip (2)of the post (1).

I claim:
 1. The combination of a radicular post and a resilient dentalimpression for use in preparing a cap to be fixed to a tooth having apost hole shaped to receive the post,the post comprising a conical partfor entering the post hole, the post having a cylindrical part whichextends from the tooth when the post is seated in the post hole and thecylindrical part having retention groove means circularly disposedaround it, and the conical part and the cylindrical part and the groovemeans being fully symmetrically disposed about the longitudinal axis ofthe post; and the impression comprising a cured resilient compoundhaving a molded hole fitting the cylindrical part of the post, and theimpression having resilient ring means in the molded hole shaped toenter and fill the groove means in the post, the shape of the groovemeans and the resilience of the impression being selected such that thecylindrical part of the post can be removed from and re-positionedwithin the molded hole in the impression without damaging the impressionand while achieving accurate positioning of the post therein because theparts of the post are symmetrical about said longitudinal axis.
 2. Themethod of preparing a dental impression for making a cap to be fixed toa tooth having a post hole shaped to receive a radicular post,comprising the steps of:installing and seating a post in the post hole,the post having a conical part for entering the post hole and having acylindrical part to project from the tooth, and the cylindrical parthaving retention groove means circularly disposed around it, and theconical and cylindrical parts being symmetrically disposed about thelongitudinal axis of the post; molding resilient impression compoundover the tooth and the projecting part of the post leaving no voids,whereby to form an impression having an internal hole fitting saidcylindrical part of the post and having ring means in the internal holefitting the groove means; and removing the molded impression and thepost from the tooth, the shape of the groove means and the resilience ofthe ring means within the impression being selected to provide areversible lock whereby in the event that the post remains in the toothduring removal of the impression a post which is identical in shape canbe reinserted and locked in the internal hole and will be properlypositioned therein during subsequent laboratory steps because the partsof the post are symmetrical about its longitudinal axis and thus have nospecific orientation in terms of angle of rotation in the impressionabout said axis.